Early Onset and Familial Gastric Cancer Registry

Inclusion Criteria: Patient/Relative Cohort: Must meet one or more criteria below: 1. A person with a diagnosis of gastric or gastroesophageal junction (GEJ) adenocarcinoma confirmed at the treating institution. 2. A person without gastric or GEJ adenocarcinoma who has or had a first degree relative eligible for a High Risk Genetic sub-group (EOGC/FGC). 1. Early Onset Gastric Cancer - diagnosis of gastric cancer before the age of 50 without a family history of the disease. 2. Familial Gastric Cancer - having a family history of gastric cancer as defined as one first degree relative or 2 second degree relatives. 3. A person without gastric or GEJ adenocarcinoma who has a personal family history of a genetic mutation associated with the development of gastric or GEJ adenocarcinoma (i.e. family history of CDH1 mutation). II. Must be willing to provide a blood sample for germline DNA. These individuals will sign the "Patient/Relative Consent". Following enrollment, we will assign individuals to the appropriate High Genetic Risk or Low Genetic Risk groups based on the age of diagnosis and their family history. Subject Exclusion Criteria Patients are ineligible for the study if they: * Have any condition, which in the opinion of the primary MSK clinician or investigators precludes their ability to provide informed consent. * Relatives of patients that are not eligible for the High Genetic Risk Cohorts who are less than 18 years of age are excluded. * Relatives of patients eligible for the High Genetic Risk Cohorts who do not have a proband available to join the study are excluded. (Unless there is a known CDH1 mutation in the family).